Shrinking ice worries Great Lakes scientists

Mar. 7, 2013

Relatively little ice is near the shoreline March 4, 2013, near Port Huron. Ice cover has decreased nearly 70% on the five Great Lakes since the early 1970s, according to the National Oceanic and Atmospheric Administration. / Matthew Dae Smith/Lansing State Journal

Written by

Louise Knott Ahern

Lansing State Journal

ABOARD THE BRISTOL BAY, Mich. — The crew of the U.S. Coast Guard cutter Bristol Bay has battled pretty much everything the Great Lakes can think up — 14-foot swells that left even experienced guardsmen heaving in the head, stranded animals that floated too far out, barges stuck in shallow shores.

The one thing they don't see as much of — at least not anymore — is ice.

One of the Detroit-based crew's primary responsibilities is ice breaking during the winter, clearing Great Lakes waterways of ice buildup so cargo ships can pass through.

Last year, the Bristol Bay didn't get called out a single time.

Though they've gone out several times this season, the number of missions are nowhere near what guardsmen from decades ago faced.

Why? Great Lakes ice is shrinking.

Ice cover has decreased nearly 70% on the five Great Lakes since the early 1970s, according to the National Oceanic and Atmospheric Administration. The five Great Lakes hold 20% of the world's fresh water and have more than 11,000 miles of shoreline.

Every one of the lakes has endured the winter meltdown:

Lake Ontario saw the most dramatic decrease with an 88% drop in ice coverage.

Lake Superior lost 76% of its ice.

Lake Michigan saw a decrease of 77%.

Lake Huron's ice has decreased 62%.

Lake Erie, the shallowest of the lakes and therefore the first to freeze every year, lost half of its ice cover.

Scientists blame global warming. Hotter days mean warmer water.

But in the case of Lake Superior, which has seen a water-temperature increase of 4 degrees in the past 25 years, the water is warming faster than the air, according to research by the Large Lakes Observatory at the University of Minnesota-Duluth.

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"When you step back and look at what's happening in the Arctic and with the Greenland ice sheet, you realize it's not just the Great Lakes," said George Leshkevich of NOAA's Great Lakes Environmental Research Laboratory. "It's happening globally."

The data is incomplete yet for this winter.

"You'll have ups and downs," Leshkevich said. "Some years you'll have more ice coverage, and some years you'll have less. But the trend line is going down. And there are a number of potential impacts of that."

Water levels

Great Lakes water levels have dropped to record lows in the past two years. While several factors affect water levels, the low levels are caused in part by a lack of ice cover during the winter.

Without adequate ice, more water evaporates, Leshkevich said. At the same time, the atmosphere picks up more water and turns it into massive lake-effect snowstorms that carry Great Lakes water elsewhere.

Low water levels create their own set of problems, not the least of which is the effect on shipping. Cargo carriers aren't able to transport as much as they used to, said Glen Nekvasil, vice president of the Lake Carriers Association. Many companies are shedding 10,000 tons or more of cargo.

Fish

Some types of fish, including whitefish and yellow perch, spawn in shallow waters and rely on ice cover to protect their eggs. Less ice means a greater threat to reproduction.

A long-term drop in the fish population would also affect the Great Lakes fishing, a $4 billion industry.

Invasive species

Adequate ice cover is crucial to killing off some invasive species and slowing their growth. When ice fails to develop, allowing waters to retain more heat than normal, certain species — most notably, zebra mussels — are able to thrive more easily.

Rising water temperatures also spur algae blooms. Algae can suck the oxygen from water, threatening fish and other aquatic species.

Erosion

A thick, solid cover of ice provides a barrier between the lakes and the shoreline. Without that protection, shores and fragile wetlands take a beating from wind and waves year-round.